The invention relates to a fuel injection pump for internal combustion engines including a simultaneously reciprocating and rotating pump piston. The pump piston serves as fuel distributor and its pressure chamber communicates via a pressure valve with a chamber formed by a screw cap which at the same time serves to clamp the valve element onto the injection pump cylinder. In such fuel injection pumps employing screw caps a reliable seal must be provided between the valve element and the screw cap, and between the valve element and the pump cylinder. In most cases the metal-to-metal seal is provided merely by an extremely tight threaded insertion of the screw cap. Inasmuch as the clamped parts are virtually unyielding, even very slight degrees of loosening suffice to break the seal.